1. Field of the Invention
The present invention relates to a vehicle rim, intended for mounting a tire and a bearing support capable of supporting the tire when the inflation pressure of the tire is low or even zero. It also relates to a tire/wheel assembly comprising such a rim and a process for mounting such a tire/wheel assembly.
2. Technical Background
Rims of this type are described, for example, in documents U.S. Pat. No. 5,787,950, U.S. Pat. No. 6,415,839 and WO 01/08905.
In the present description, an assembly comprising a wheel, a tire mounted on a wheel and a tread bearing support is designated by “tire/wheel assembly”. The wheel comprises a rim and a disc.
In the tire/wheel assemblies of the field of the invention, the beads of the tire bear on seats of the rim and the mean diameters of the two seats are different in order to facilitate mounting and demounting of the bearing support on/from the rim.
The bearing support is born circumferentially by a supporting bearing surface of the rim, located between the two seats. It is formed for example from an elastically deformable elastomeric material, which prevents the tread from sagging when the tire/wheel assembly is operating in extended mode. “Rolling in extended mode” is understood to mean rolling of a tire the inflation pressure of which is abnormally low compared with the nominal pressure of use of the tire, the inflation pressure possibly even being zero.
The bearing support is mounted by sliding on axially, as described in detail in document US 2004/0074610. The different steps of mounting according to the prior art are illustrated in FIG. 8 below.
When a bead of the tire is under great stress, it may be induced to leave its bearing seat. According to whether it leaves its seat towards the inside of the rim (that is to say, to lodge in the space between the two seats) or towards the outside (that is to say, losing any contact with the rim), the term used will be “unseating” or “rolling off”.
To evaluate the resistance of a rim to unseating, a tire/wheel assembly comprising this rim can be subjected to different tests when rolling in extended mode, in particular to a test at zero pressure. Automobile manufacturers generally demand that the resistance to unseating be demonstrated on a front train upon sustained emergency braking during sustained cornering.
Tests performed on the rim described in document WO 01/08905 have shown that this rim perfectly satisfies current manufacturers' demands in terms of resistance to unseating. The safety hump therefore suitably fulfils its role.
The inventors of the present invention carried out even more demanding rolling tests at zero pressure and noted that the bead, when subjected to very high forces in exceptional situations of the type when traveling on a circuit, may still become unseated. When a rim provided with a “ledge” (reference 53 of FIG. 3) and a weight reduction groove (reference 55 of FIG. 3) is used, the bead may cross the entire ledge and drop into the weight reduction groove.